Oxidation characteristics of RU/CeO2 were investigated by N2O decomposition in the presence Of C3H6, by temperature programmed desorption (TPD), IR, and XAFS measurements using C3H6 as a probe molecule. Ru/CeO2 (Ru: 5 wt%) had highly dispersed Ru species which formed Ru-O-Ce and Ru=O bonds. This Ru species was in the five-coordination environment and reacted rapidly with allylic hydrogen Of C3H6, providing its double bond oxygen. The Ru=O site was easily regenerated under oxygen atmosphere. This type of metal-oxo species was not formed for Pt, Pd, and Rh on CeO2. The peculiar oxidation property of Ru/CeO2 catalyst was due to the Ru=O species. The optimal preparation procedure for producing Ru=O species was to support Ru on hydrated Ce(OH)(3) without drying or calcinations. The saturated amount of Ru=O species was 2 wt% loading of Ru. (c) 2005 Elsevier B.V. All rights reserved.